Engineering & Mining Journal

AUG 2017

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Page 37 of 99

BLASTING
36 E&MJ • AUGUST 2017 www.e-mj.com
The burn cut, otherwise known as a par-
allel hole cut, is one of the most com-
monly used underground blasting meth-
ods because it can be used in drifts of all
sizes and dimensions. The burn cut has
also been tested in almost all rock types
and can effectively break weak or strong
rocks, depending on the design. In a burn
cut round, five different classifications of
holes exist that work together to create a
round, which pulls effectively, leaves a
good contour and is cost-effective.
The first of these holes is the relief
holes (red box in Figure one) and are not
loaded with explosives. These holes act
as a relief point for the surrounding rock
to break to, and they are normally larger
in diameter, with both the diameter and
the length of the hole controlling the total
face advance of the round.
The second type of hole is the cut hole
(green box in Figure one) and these holes
are loaded with explosives and closely
spaced to the relief holes. These are also
the first holes to fire in a round and smash
and eject the rock between them and the
relief holes. Depending on the round, mul-
tiple layers of cut holes may exist, which
will continue increasing the relief in the
round. These holes tend to be discussed
as "overloaded" because they have much
more explosives in them than needed to
break a very small amount of rock.
The third type of hole is the production
hole (yellow box in Figure one) and these
holes are those that are now properly loaded
for the amount of rock that they will break.
By the time the production holes start to
fire, all the cut holes should be fired and a
large enough cut should be opened for pro-
duction holes to break to. One critical thing
to consider before deciding to switch to the
production holes is: Will the open cut cre-
ated be able to handle the total volume of
material created by the production holes? If
a hole fires and, after swelling, the extra vol-
ume of material is larger than the open cut,
then the round will freeze and the remain-
der of the round will not break as intended.
The fourth type of hole is the lifter
hole (not pictured) and is drilled on the
floor and loaded with explosives to break a
smooth line along the bottom of the floor.
These are typically closely spaced and
fired after the production holes with simi-
lar mechanics to a trim shot, but are nor-
mally heavily loaded to maintain grade.
The fifth type of hole is the Contour
Holes (not pictured), which are drilled
Modern Burn Cut Design
By Anthony Konya, Dr. Calvin J. Konya and Dr. Paul Worsey
Figure 1 — Burn round hole types (taken underground
at S&T Experimental mine).